class Computer:
    def __init__(self, num1, num2):
        self.num1 = num1
        self.num2 = num2

    def addition(self):
        return self.num1 + self.num2

    def subtraction(self):
        return self.num1 - self.num2

    def multiplication(self):
        return self.num1 * self.num2

    def division(self):
        if self.num2 != 0:
            return self.num1 / self.num2
        else:
            print("除数不能为零！")
            return None


computer = Computer(4, 8)
print(computer.addition())
print(computer.subtraction())
print(computer.multiplication())
print(computer.division())